We propose investigations in five areas aimed ultimately at elucidating a potential human hormone-related role for T-strain pathogenicity. (1) Efforts to improve laboratory cultural conditions in order to provide a reliable diagnostic medium for the isolation of T- strain mycoplasmas and their growth in numbers high enough to permit better physiological studies. (2) Studies on the energy metabolism of T-strain mycoplasmas will provide insight into T-strain-host cell interaction. Our previous results imply a search for such enzymes as urease, ATP: urea amidolyase, allantoicase, putrescine transcarbamoylase, ornithine decarboxylase, agmatine ureohydrolase and proteases. (3) Development of a defined growth medium will be pursued and based on our observation that T-strain mycoplasmas can be grown in a medium where the only undefined component is serum fraction V. Replacement of fraction V with a defined protein (known amino acid sequence) will be the ultimate aim. (4) Studies on T-strain mycoplasma interactions with a variety of human cell and organ cultures in vitro. (5) T-strain pathogenesis will be studied in vivo using animal model systems.